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RvB

Is it likely to be an 02 sensor?

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My lad's 2003 Arosa 1.4 Sport brought the engine management light on a couple of days ago. Car was running fine before it came on and after too. I've put vag com on it and got this:

1 Fault Found:
16804 -  Catalyst System; Bank 1: Efficiency Below Threshold
        P0420 - 35-00 -  

 

I've cleared the code and driven it about 10 miles and the eml hasn't come back on yet. I've checked for exhaust leaks and can't see/hear anything, so I'm wondering if the knowledgeable folk of clublupo have come across this one before. Do the o2 sensors fail with age on these cars or is it more likely the cat itself?

We got the car in November and it hasn't done a lot of miles since as he's still learning to drive, in fact it hasn't done a lot of miles in the last few years as the previous owner only did about 1200 miles a year and so did the previous owner to that. So I'm hoping it's just gunged up and a few good spirited drives will clear it out a bit, but if not any ideas where to look?

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I've had these where the light comes on around every 5k and will go off by itself within 100 miles.

I call it character.

Not that helpful but it doesn't do any harm.

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Spirited drive will probably fix it.

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Lots of start stop driving and frequent cold starts can cause the cat to clog up. A 30 minute steady run on the motorway will clean it out.

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5 hours ago, RvB said:

Thanks. It's got a fresh tank of momentum 99 all ready for a good blast, so will see how it goes.

Stick some redex in when you get down to about the last quarter of the tank. Thrash the arse off it.

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Momentum 99 has the same stuff in as redex apparently (according to the people i know at castrol/bp research).

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5 hours ago, Skezza said:

Stick some redex in when you get down to about the last quarter of the tank. Thrash the arse off it.

Redex that takes me back 20 years or so,just watched firth gear on YouTube with it,think I will use a bottle good stuf.

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There's certainly something different with momentum, whenever I put it in my Abarth it gives the exhaust vapour a very parafinny type smell and makes it pop and fart a bit more. Don't get that smell with vpower or regular unleaded.

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Revisiting this for some more input, if I may.

Car has now done about 600 miles since I initially posted, so several tanks of fuel and several  "spirited" drives. And it's been doing 25 mile dual carriage way runs at around 70-80 mph twice a day for the last couple of weeks. I've also put a bottle of cataclean in it.

BUT the light still keeps coming on, the fault code is the same every time. When I clear the fault code it stays away for about 80 miles and then comes back.

So what do we think, worth persevering, or look at o2 sensors, cat etc? or something else?

 

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Calculate your mpg and see if there's a negative effect there 

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36 minutes ago, Rich said:

Calculate your mpg and see if there's a negative effect there 

It's around 38-40 mpg, which I would have said was okay.

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1 minute ago, Sausage said:

original cat or aftermarket?

There is some readiness tests in vagcom apparently for the o2 sensors.http://www.vwaudiforum.co.uk/forum/showthread.php/176472-Lambda-ageing-test

http://wiki.ross-tech.com/wiki/index.php/16804/P0420/001056

I'd say original. There's a load of history with the car, there's a receipt for the secondary cat and front exhaust section in 2013, but don't see anything for the main manifold cat. Looking at it it looks original and untouched around that area.

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You can use VAGCOM (VCDS) to diagnose the Lambda voltage. If you start graphing the voltage from stone cold, you should see it rise then change from open loop to closed loop control, once warm. It should hover around 0.7V from memory. When rich, it goes down, lean goes up (more oxygen). 

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15 minutes ago, mk2 said:

You can use VAGCOM (VCDS) to diagnose the Lambda voltage. If you start graphing the voltage from stone cold, you should see it rise then change from open loop to closed loop control, once warm. It should hover around 0.7V from memory. When rich, it goes down, lean goes up (more oxygen). 

image.png.1fc687980a2ae403074282f94729535b.png

I take it that's Block 031 you're talking about there? I haven't looked at these yet, will have a go later along with the ageing test  that Sausage mentioned.

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I honestly dont know without having vcds in front of me. By the way, some of the label files can be wrong, so you think you're looking at one sensor, whereas the readings you're seeing are actually from something completely different!

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I would be tempted to chuck a new sensor in. They do go bad and apparently it is just a delicate foil inside. I recall hearing they can even break if dropped. My Gti had the same fault flashing up, new sensor fixed it.

If the Arosa is a keeper go for a decent brand such as Bosch or NGK (part of NGK group) other wise go cheap to test if the fault clears and expect to replace more often

 

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Not a 100% on what these VCDS tests are telling me (if anything!), other than the cat test failed.

Measuring block tests.

 001-002.PNG.2e86ec65810bddc3c50bd27c119b265d.PNG 

030-032.PNG.a1e950bc7d5f3e7682749af23eb8e36c.PNG

The -20% Lambda adaption would indicate running rich would it not?

032-033.PNG.42038f1c8503fd60942ce905b2ad694c.PNG

 

The sensor tests

034-1.PNG.d27bbd37b31ec1243bac094cc98a8e7b.PNG

 

034-2.PNG.c4a3156e334f3b352ff8852b6508619e.PNG

036-1.PNG.d187a43ded3414f38f9e09096459057a.PNG

036-2.PNG.811a27b2ff0858b9312a9812db0fbc23.PNG

 

And finally the cat test which seems conclusive! Unless one of the sensors isn't reading right?

046-1.PNG.261bb5370ecd30a8dfcc84306c7c3f9d.PNG

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your engine loading should be a lot lower for idle. it;s telling you that 11% of your available engine power is being used!

cat temp should be 600+

injection timing should be about 1.2-1.6 for idle for hot engine (unless loaded with AC or something)

manifold pressure should be lower too. you want a fairly high vacuum at warm idle.

it could be an air leak (as in extra air is being sucked in somewhere). Not convinced the cat or the O2 sensor are toast. they're pretty tough.

i'd be tempted to pop down to the local mot place and ask them to just have a sniff with their gas analyser for a minute. that'd be ultimate proof of whats coming out of the tail pipe. hydrocarbons are all you're interested in. if high, then it could be the cat. if low/normal then something to do with the fuelling/air system.

 

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http://wiki.ross-tech.com/wiki/index.php/Fuel_Trim_Info

Group 32: -20% means running rich.

Quote" In general, an out-of-spec value in the first field (Additive) indicates a vacuum leak since it is mostly present at idle, when vacuum is highest. An out-of-spec value in the second field (Multiplicative) indicates a fault at higher RPM, and may point to a faulty MAF. 

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Thanks for looking.

 

50 minutes ago, Sausage said:

http://wiki.ross-tech.com/wiki/index.php/Fuel_Trim_Info

Group 32: -20% means running rich.

Quote" In general, an out-of-spec value in the first field (Additive) indicates a vacuum leak since it is mostly present at idle, when vacuum is highest. An out-of-spec value in the second field (Multiplicative) indicates a fault at higher RPM, and may point to a faulty MAF. 

Yeah, that's what I thought.

 

53 minutes ago, mk2 said:

your engine loading should be a lot lower for idle. it;s telling you that 11% of your available engine power is being used!

cat temp should be 600+

injection timing should be about 1.2-1.6 for idle for hot engine (unless loaded with AC or something)

manifold pressure should be lower too. you want a fairly high vacuum at warm idle.

it could be an air leak (as in extra air is being sucked in somewhere). Not convinced the cat or the O2 sensor are toast. they're pretty tough.

i'd be tempted to pop down to the local mot place and ask them to just have a sniff with their gas analyser for a minute. that'd be ultimate proof of whats coming out of the tail pipe. hydrocarbons are all you're interested in. if high, then it could be the cat. if low/normal then something to do with the fuelling/air system.

 

What would a healthy manifold pressure at idle be?  I'll go through all the vacuum pipes at the weekend.

if an o2 sensor is giving a false reading surely this would be telling the ecu the wrong info too though?

 

 

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Right, went though all the pipes and joints I could find squirting some carb cleaner around any joints listening and watching vcds. Can't find any thing leaking!

So I bit the bullet and got a cheap upstream o2 sensor to try. The trims look much more sensible now with the new sensor.

032.png.66014b430240343fdb3f14f03c0b33e0.png

Exhaust and cat temps are higher now too, although manifold pressure is still around 300mbar.

So we'll see what happens and if the light stays out!

 

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Yeah, keep us up to date if anything changes. Sounds good though. Unusual for an upstream sensor to go. They're pretty tough.

Just got me thinking... I'm not 100% sure, but I think the upstream and downstream O2 sensors are interchangable. Both are narrow band type. The difference is the cable length but both use the same connector types. If feeling enthusiastic, you could try swapping around things (and use the old sensor) to be 100% sure it was the sensor. Just make sure the downstream signal plugs into the downstream loom cable. Same for the upstream if they are they same connectors (rounded rectangular with 4 pins).

Edited by mk2

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